The neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha, 5alpha-Por allopregnanolone) is a potent positive modulator of GABAA receptors. Consistent with the speculation that 3alpha, 5alpha-P may represent a physiologically significant neuromodulator, preliminary studies in the selectively bred Withdrawal Seizure-Prone (WSP) and- Resistant (WSR) mice found that lower endogenous levels of, or decreased sensitivity to, 3alpha, 5alpha-P may be correlated with increased ethanol (EtOH) withdrawal severity. In EtOH-withdrawing WSPs, the reduced sensitivity to 3alpha, 5-alpha-P, as well as the decrease in endogenous 3alpha, 5alpha-P. This would lead to greater neural excitability in the WSP line during EtOH withdrawal. The present proposal will use a multi-disciplinary approach to test the hypothesis that genetic differences in EtOH withdrawal severity are due in part, to alterations in sensitivity, to and/or biosynthesis of, 3alpha, 5-alpha-P. Studies related to Specific Aims 1 and 2 will determine the temporal relationship between EtOH withdrawal severity and the chronic EtOH- induced alterations in endogenous 3alpha, 5alpha-P concentration and activity and/or gene expression of the 3alpha, 5alpha-P biosynthetic enzyme, 5alpha-reductase. The physiological consequences of 5alpha- reductase inhibition during EtOH withdrawal will be examined in Specific Aim 2. Studies related to Specific Aims 4 and 5 will determine the correspondence between behavioral sensitivity to 3alpha, 5alpha-P and functional sensitivity of GABAA receptors to 3alpha, 5alpha-P. The combined use of behavioral, biochemical and molecular strategies will determine the importance of 3alpha, 5alpha-P as a neuromodulator of EtOH withdrawal severity. Further, the demonstration of selected line differences in sensitivity to, and/or biosynthesis of, 3alpha, 5alpha-P during EtOH withdrawal will provide additional evidence that altering the local neuroactivity steroid environment in the brain can differentially modulate GABAA receptors (i.e., WSP and WSR) and lead to the greater neural excitability in the WSP versus WSR line during EtOH withdrawal. The long term goal of this research is to understand mechanisms underlying how deleterious responses to chronic alcohol (i.e., physical dependence leading to withdrawal seizures) are regulated at the genetic level. Not only will this information aid in our understand of the mechanisms underlying alcohol withdrawal, but this knowledge would help in the development of new strategies for the treatment of alcohol dependence.